Silencing a Noisy Switch

The Linksys SR224G is a 24-port network switch. A bit excessive for what I needed, but I couldn’t resist the price of £4.99 on ebay. One problem – very noisy indeed. This would be fine in it’s normal environment, a rack full of other noisy equipment but I wanted it in my office, because that’s where most of the Cat5 cabling in the house terminates.

The source of the racket was the two cooling fans, so the first thing I did (once I figured out how to get the case open) was disconnect them. I decided it didn’t need all that cooling, because it wasn’t stuffed into a rack in a hot room, with lots more hot things above and below it, it was free-standing on a desk. Also I wouldn’t be putting all that much load on it. I ran it for a day without the fans, and I couldn’t detect any excess heat building up at all, but it seemed wrong to have no cooling at all.

The two power connectors on the motherboard are 5V, but the nice silent (a marketing term meaning quiet-ish) fan I had wanted 12V. I thought it might work run at 5V, albeit slowly, and it did – but only with a manual kickstart. As I didn’t want to have to be around to do that after a power failure, I needed 12V. Unfortunately the power supply in the switch only supplies 3.3V and 5V, so the power had to come from somewhere else.

I had a 3.5mm jack socket lying around – probably the worst possible option, as will become apparent, but the only option at the time. I ‘drilled’ (with my penknife) a hole in the metal case and fitted it there. Only then did I realise that the metal barrel of the socket is connected to one of the terminals, so I’d be connecting the chassis AC ground to the power input’s DC ground, which seemed like a bad idea.

This picture shows it up and running, using a Sinclair ZX81 power supply, which happens to (insanely, if you ask me) also use a 3.5mm jack. This was good for a test, but a) I need that PSU for the ZX81 (no, really!), b) it’s only 9V, and c) I don’t want a another hot energy-wasting thing taking up yet another mains socket.

There is a perfect source of 12V nearby though, in the form of a PC that’s always on. I bodged together a cable and hooked it up. The first problem was that the ATX power supply in the PC immediately shut itself down in an act of self preservation when I connected it up. This was quite puzzling, until I re-opened the switch case and noticed that the inside of the plastic front panel was a strange non-plasticy copper colour. I tested it, and it was conductive – some kind of spray on stuff, which I scraped off from the area surrounding the socket.

The only other problem is the 3.5mm jack – it’s almost impossible to insert one of these without momentarily shorting the contacts on the plug. I guess the ZX81 power supply doesn’t mind this, but an ATX power supply does, and instantly shuts down. That means that as it stands I can’t take that plug in or out of the switch’s front panel without rudely powering off the server, which is not ideal. At some point I might use a different kind of socket, although another idea I had in mind was to power the switch entirely from the ATX power supply, since it already supplies the 3.3V and 5V needed for the switch itself, as well as the 12V for the fan.

Anyway, the end result is that the switch, which previously sounded like a hoover, is almost completely silent.